1. Field of the Invention
The present invention relates to a battery pack voltage equalization method, and more particularly, to a passive balancing method for battery packs.
2. Description of Related Art
Rechargeable batteries have now been widely used to provide electrical power to a variety of electronic products. The terminal voltage or capacity of a signal battery (cell) is limited. A battery pack which is composed by a plurality of rechargeable battery cells connected in series is used in electronics such as laptops to increase the output voltage and charge capacity. The charging/discharging capacity, charging conversion efficiency, or initial capacity of each battery cell within the same battery pack could be inconsistent to each other. Therefore, after repeated charging and discharging processes in a long term, the discrepancies among each battery cell may be amplified, so that the performance of the battery pack becomes more and more limited by battery cells with poor characteristics.
In order to increase the lifetime of the battery pack and reduce the above-mentioned problem, a battery equalization mechanism is provided in many battery management systems, such as a passive balancing method, which takes the lowest voltage among all of the battery cells of the battery pack as a reference voltage and consuming the electricity of batteries with voltage higher than the reference voltage by resistor into heat for dissipating, so that each battery cell of the battery pack may initiate to charge from the same voltage, so as to solve the issues of that battery cells with poor characteristics may not be fully charged.
However, the conventional passive battery balancing method does not consider the discrepancies of maximum discharging/charging capacities among each of the battery cells, yet take the same reference voltage to determine the balancing criteria for different battery cells. The conventional method often causes the battery cells with better performance in the battery pack to be limited by the battery cells with poor performance during the equalization process. Moreover, such method doesn't take the battery aging factor into consideration.